Mitch Marsh's injury a concern for Aussies

Australia face the prospect of losing arguably their form player for the third Test against South Africa, with Mitch Marsh nursing a groin strain.

The surprise injury Australia can hardly afford

Port Elizabeth proved an unhappy hunting ground for Marsh, who also endured a gastro bug and was fined 20 per cent of his match fee for swearing at Kagiso Rabada after the paceman bowled him on Monday.

But it is the groin injury that will leave the West Australian racing the clock to prove his fitness for the clash that starts on Thursday week in Cape Town.

"Reasonably confident but we'll see over the next couple of days. Medical staff will have a look at him," coach Darren Lehmann said.

"We're hopeful for the next Test."

Marsh's setback is minor but an obvious concern for the tourists, who suffered a six-wicket loss in the second Test.

Peter Handscomb is the reserve batsman in the squad but selectors may opt to summon a like-for-like cover player for Marsh, such as Marcus Stoinis.

"It sort of depends what we want and what we could get in Cape Town. We'll have to sum that up the next couple of days, once we get there and have a look," Lehmann said.

Mitch Marsh. Pic: Getty

Marsh's knock of 96 in the first Test set the platform for Australia's 118-run win, while his resistance late on day three of the second Test gave Australia some hope of setting a more imposing target than their eventual 101.

The 26-year-old has become Australia's middle-order rock since his Ashes recall, with David Warner the only Australian to have scored more runs than him in the current series.

"He's looking as good as anyone at the moment," Lehmann said.

"He was (also) important for us with those couple wickets late on day two."

Steve Smith is also upbeat Marsh, who was stationed initially stationed at first slip on Monday because of his lack of mobility, will be fit for the third Test.

"It's a good break between now and the next Test match and he's telling me he'll be fine, but we'll wait and see how things go," Smith said.

Lehmann and Smith both suggested star pacemen Mitchell Starc, Josh Hazlewood and Pat Cummins are all in good shape and should be fit for the third Test.

"All the quicks are going really well," Smith said.

"Hopefully with a good 10-day break they can freshen up a little bit."